Systems and methods for bonding semiconductor elements

ABSTRACT

A method of ultrasonically bonding semiconductor elements includes the steps of: (a) aligning surfaces of a plurality of first conductive structures of a first semiconductor element to respective surfaces of a plurality of second conductive structures of a second semiconductor element, wherein the surfaces of each of the plurality of first conductive structures and the plurality of second conductive structures include aluminum; and (b) ultrasonically bonding ones of the first conductive structures to respective ones of the second conductive structures.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation application of application Ser. No.15/147,015, filed May 5, 2016, now U.S. Pat. No. 9,633,981, which is adivisional of application Ser. No. 14/822,164, filed Aug. 10, 2015, nowU.S. Pat. No. 9,362,247, which is a continuation application ofapplication Ser. No. 14/505,609 filed Oct. 3, 2014, now U.S. Pat. No.9,136,240, which claims the benefit of Provisional Application No.61/888,203, filed Oct. 8, 2013, the content of each of which isincorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to the formation of semiconductorpackages, and more particularly, to improved systems and methods forbonding semiconductor elements together.

BACKGROUND OF THE INVENTION

Traditional semiconductor packaging typically involves die attachprocesses and wire bonding processes. Advanced semiconductor packagingtechnologies (e.g., flip chip bonding, thermo-compression bonding, etc.)technologies are gaining more traction in this industry. For example, inthermo-compression bonding, heat and pressure are used to form aplurality of interconnections between semiconductor elements.

While advanced packaging technologies are increasingly utilized thereare many limitations in these technologies including, for example,limitations related to the relative infancy of some advanced packagingtechnologies. Thus, it would be desirable to provide improved systemsfor, and methods of, bonding semiconductor elements together.

SUMMARY OF THE INVENTION

According to an exemplary embodiment of the present invention, a methodof ultrasonically bonding semiconductor elements is provided. The methodincludes the steps of: (a) aligning surfaces of a plurality of firstconductive structures of a first semiconductor element to respectivesurfaces of a plurality of second conductive structures of a secondsemiconductor element, wherein the surfaces of each of the plurality offirst conductive structures and the plurality of second conductivestructures include aluminum; and (b) ultrasonically bonding ones of thefirst conductive structures to respective ones of the second conductivestructures.

According to another exemplary embodiment of the present invention, asemiconductor device is provided. The semiconductor device includes: (a)a first semiconductor element including a plurality of first conductivestructures, at least a contact portion of each of the plurality of firstconductive structures including aluminum; and (b) a second semiconductorelement including a plurality of second conductive structures, at leasta contact portion of each of the plurality of second conductivestructures including aluminum. The contact portions of ones of theplurality of first conductive structures are in contact with, and areultrasonically bonded to, respective ones of the contact portions of theplurality of second conductive structures.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is best understood from the following detailed descriptionwhen read in connection with the accompanying drawings. It is emphasizedthat, according to common practice, the various features of the drawingsare not to scale. On the contrary, the dimensions of the variousfeatures are arbitrarily expanded or reduced for clarity. Included inthe drawings are the following figures:

FIGS. 1A-1C are block diagram views of portions of an ultrasonic bondingmachine illustrating a structure and method of bonding an uppersemiconductor element to a lower semiconductor element in accordancewith an exemplary embodiment of the present invention;

FIG. 2A is a block diagram view of portions of an ultrasonic bondingmachine illustrating a structure and method of bonding an uppersemiconductor element to a lower semiconductor element in accordancewith another exemplary embodiment of the present invention;

FIG. 2B is an enlarged view of portion “FIG. 2B” of FIG. 2A;

FIG. 2C is a view of FIG. 2B after ultrasonic bonding;

FIG. 3 is a block diagram view of portions of an ultrasonic bondingmachine illustrating a structure and method of bonding an uppersemiconductor element to a lower semiconductor element in accordancewith yet another exemplary embodiment of the present invention;

FIG. 4A is a block diagram view of portions of an ultrasonic bondingmachine illustrating a structure and method of bonding an uppersemiconductor element to a lower semiconductor element in accordancewith another exemplary embodiment of the present invention;

FIG. 4B is an enlarged view of portion “FIG. 4B” of FIG. 4A;

FIG. 4C is a view of FIG. 4B after ultrasonic bonding;

FIG. 5A is a block diagram view of portions of an ultrasonic bondingmachine illustrating a structure and method of bonding an uppersemiconductor element to a lower semiconductor element in accordancewith another exemplary embodiment of the present invention;

FIG. 5B is an enlarged view of portion “FIG. 5B” of FIG. 5A;

FIG. 5C is a view of FIG. 5B after ultrasonic bonding;

FIG. 6A is a block diagram view of portions of an ultrasonic bondingmachine illustrating a structure and method of bonding an uppersemiconductor element to a lower semiconductor element in accordancewith yet another exemplary embodiment of the present invention;

FIG. 6B is an enlarged view of portion of “FIG. 6B” of FIG. 6A;

FIG. 6C is a view of a portion of FIG. 6A after contact betweenconductive structures; and

FIG. 7 is a flow diagram illustrating a method of ultrasonically bondingsemiconductor elements in accordance with an exemplary embodiment of thepresent invention.

DETAILED DESCRIPTION OF THE INVENTION

As used herein, the term “semiconductor element” is intended to refer toany structure including (or configured to include at a later step) asemiconductor chip or die. Exemplary semiconductor elements include abare semiconductor die, a semiconductor die on a substrate (e.g., aleadframe, a PCB, a carrier, etc.), a packaged semiconductor device, aflip chip semiconductor device, a die embedded in a substrate, a stackof semiconductor die, amongst others. Further, the semiconductor elementmay include an element configured to be bonded or otherwise included ina semiconductor package (e.g., a spacer to be bonded in a stacked dieconfiguration, a substrate, etc.).

In accordance with certain exemplary embodiments of the presentinvention, inventive techniques (and structures) are provided forassembling a semiconductor device such as a package on package (i.e.,PoP) structure. For example, a plurality of semiconductor elements(which may be packages) may be arranged in a stacked configuration. Eachof the elements desirably includes aluminum (or aluminum alloy, orpartially aluminum) conductive structures that are ultrasonically bondedtogether. Such a technique has certain advantages including, forexample: a reduced density compared to other interconnection techniques(e.g., solder based PoP techniques); no solder mass reflow utilized incontrast to other interconnection techniques; and room temperatureultrasonic bonding enabled in certain applications through the use of analuminum to aluminum interconnect.

FIG. 1A illustrates portions of ultrasonic bonding machine 100,including bonding tool 124 and support structure 150. As will beappreciated by those skilled in the art, a thermo-compression bondingmachine (such as machine 100, or any of the other machine embodimentsdescribed herein) may include many elements not shown in the drawingsherein for simplicity. Exemplary elements includes, for example: inputelements for providing input workpieces to be bonded with additionalsemiconductor elements; output elements for receiving processedworkpieces that now include additional semiconductor elements; transportsystems for moving workpieces; imaging systems for imaging and alignmentof workpieces; a bond head assembly carrying the bonding tool; a motionsystem for moving the bond head assembly; a computer system includingsoftware for operating the machine; amongst other elements.

Referring again to FIG. 1A, upper semiconductor element 108 is retained(e.g., by vacuum, such as through vacuum ports defined by the holdingsurface of holding portion 110) by holding portion 110 of bonding tool124. Upper semiconductor element 108 includes upper conductivestructures 112 a, 112 b on a lower surface thereof. Lower semiconductorelement 160 includes semiconductor die 102 bonded to (or otherwisesupported by) substrate 104. Lower conductive structures 106 a, 106 bare provided on an upper surface of lower semiconductor die 102.Substrate 104 in turn is supported by support structure 150 (e.g., aheat block of machine 100, an anvil of machine 100, or any other desiredsupport structure). In the configuration shown in FIG. 1A (preparing forbonding), each of upper conductive structures 112 a, 112 b are generallyaligned with opposing respective lower conductive structures 106 a, 106b. Semiconductor element 108 is moved downward through the motion ofbonding tool 124 (as shown by the arrows 126 in FIG. 1A). Following thismotion, FIG. 1B illustrates contact between the respective conductivestructures 106 a, 112 a and 106 b, 112 b. Ultrasonic energy 114 isapplied to upper semiconductor element 108 and upper conductivestructures 112 a, 112 b through bonding tool 124 using an ultrasonictransducer (not shown but indicated in the drawings as “USG”, that is,ultrasonic generator). For example, an ultrasonic transducer thatcarries bonding tool 124 may in turn be carried by a bond head assemblyof machine 100.

During the ultrasonic bonding, lower conductive structures 106 a, 106 bmay be held relatively stationary through the support of lowersemiconductor element 160 by support structure 150 (e.g., a supportsurface of support structure 150 may include one or more vacuum ports tosecure substrate 104 to support structure 150 during bonding).Ultrasonic energy 114 (along with optional bond force and/or heat) maycause partial deformation of the conductive structures. For example,conductive structures 106 a, 106 b and 112 a, 112 b are illustrated asbeing partially deformed in FIG. 1C. Ultrasonic bonds are formed betweenrespective pairs of conductive structures in FIG. 1C. For example,ultrasonic bond 128 a is formed between deformed conductive structures112 a′/106 a′, and ultrasonic bond 128 b is formed between deformedconductive structures 112 b′/106 b′. Conductive structures 106 a, 106 b;112 a, 112 b may be formed of aluminum, or aluminum alloys, or maycontain aluminum at their bond surfaces, etc.

The respective pairs of conductive elements 106 a, 112 a; 106 b, 112 bmay be bonded together at room temperature (without heat being addedduring the bonding process). Optionally, additional heat may be applied,for example, to: (1) upper semiconductor element 108 through bondingtool 124, thus heating upper conductive elements 112 a, 112 b during thebonding process; and/or (2) lower semiconductor element 160 throughsupport structure 150 (e.g., heat block 150), thus heating lowerconductive structures 106 a, 106 b during the bonding process. Suchoptional heating (e.g., through the bond tool and/or the supportstructure, etc.) is applicable to any of the embodiments of the presentinvention illustrated and described herein.

Semiconductor elements 160 and 108 illustrated in FIGS. 1A-1C may be anyof a number of semiconductor elements configured to be bonded together.In one very specific example (which may also be applied to the otherembodiments illustrated and described herein) semiconductor element 160is a processor (e.g., a mobile phone processor which may also be knownas an APU (application processor unit)) and semiconductor element 108 isa memory device configured to be bonded to the processor as shown inFIGS. 1A-1C.

The conductive structures (i.e., 112 a, 112 b, 106 a, 106 b) shown inFIGS. 1A-1C are illustrated as generic structures. These structures maytake many different forms such as conductive pillars, stud bumps (e.g.,formed using a stud bumping machine), electroplated conductivestructures, sputtered conductive structures, wire portions, bond pads,contact pads, among many others. Various of the other drawings providedherein illustrate specific examples of such structures. In accordancewith certain embodiments of the present invention the conductivestructures include aluminum at the contact region (i.e., the bondingsurface) where they will be bonded to another conductive structure. Insuch embodiments, the conductive structures may be formed of aluminum,or an aluminum alloy (e.g., aluminum alloyed with copper, aluminumalloyed with silicon and copper, etc.). In other examples, theconductive structures may include a base conductive material other thanaluminum (e.g., copper) with aluminum (or aluminum alloy) at the contactregion. Throughout the present application, if a conductive structure isreferred to as being “aluminum” it is understood that the structure maybe aluminum, may be an aluminum alloy, or may include aluminum (or analuminum alloy) at a contact region of such conductive structure.

FIG. 2A illustrates portions of ultrasonic bonding machine 200,including bonding tool 224 and support structure 250. Uppersemiconductor element 208 is retained (e.g., by vacuum) by holdingportion 210 of bonding tool 224, and includes upper conductivestructures 222 a, 222 b (i.e., conductive aluminum pads 222 a, 222 b)provided at a lower surface thereof. Lower semiconductor element 260includes semiconductor die 202 bonded to (or otherwise supported by)substrate 204. Lower conductive structures 206 a, 206 b are provided onan upper surface of lower semiconductor die 202. Substrate 204 in turnis supported by support structure 250. In the configuration shown inFIG. 2A, each of upper conductive structures 222 a, 222 b are generallyaligned with (and configured to be ultraonically bonded to) opposingrespective lower conductive structures 206 a, 206 b. Lower conductivestructure 206 a includes copper (Cu) pillar 230 provided on an uppersurface of lower semiconductor die 202, and an upper aluminum contactstructure 216 on an upper surface of Cu pillar 230. Upper aluminumcontact structure 216 may be, for example, electroplated or sputteredonto the upper surface of lower copper pillar 230. FIG. 2B is anenlarged view of portion “B” of FIG. 2A and illustrates the top of lowerconductive structure 206 a at contact with upper conductive element 222a.

Ultrasonic energy is applied to upper semiconductor element 208 throughbonding tool 224 using an ultrasonic transducer (not shown). Ultrasonicenergy may cause partial deformation of the conductive structures asillustrated in FIG. 2C. That is, ultrasonic bond 228 is formed betweendeformed upper conductive structure 222 a′ and deformed contactstructure 216′ (as illustrated in FIG. 2C).

As will be appreciated by those skilled in the art, Cu pillar 230(including electroplated or sputtered aluminum contact structure/portion216) is just one example of a conductive structure including aluminum.FIG. 2A also illustrates another exemplary conductive structure 206 b.Lower conductive structure 206 b is an aluminum structure (or aluminumalloy structure) such as a portion of aluminum wire (that may be bondedusing a wire bonding process), an aluminum pillar, etc.

FIG. 3 illustrates portions of ultrasonic bonding machine 300, includingbonding tool 324 and support structure 350. Upper semiconductor element308 is retained (e.g., by vacuum) by holding portion 310 of bonding tool324, and includes upper conductive structures 322 a, 322 b (i.e,conductive aluminum pads 322 a, 322 b). FIG. 3 illustrates the bondingof a packaged semiconductor device 360 (i.e., lower semiconductorelement 360) to upper semiconductor element 308. Lower semiconductorelement 360 includes semiconductor die 302 bonded to (or otherwisesupported by) substrate 304. Lower conductive structures 306 a, 306 bare provided on an upper surface of substrate 304. Substrate 304 in turnis supported by support structure 350. Wire loops 320 a, 320 b arebonded between semiconductor die 302 and substrate 304 (while not shownin FIG. 3, die 302 may be flip chip bonded to substrate 304 as opposedto, or in addition to, the wire loop interconnections). Acoating/encapsulation 334 (such as a epoxy molding compound) has beenapplied over die 302 and wire loops 320 a, 320 b. As illustrated, theupper portions of lower conductive structures 306 a, 306 b are exposedabove coating/encapsulation 334 to permit electrical connection to uppersemiconductor element 308.

In the configuration shown in FIG. 3, each of upper conductivestructures 322 a, 322 b are generally aligned with (and configured to beultrasonically bonded to) opposing respective lower conductivestructures 306 a, 306 b. As illustrated in FIG. 3, each of lowerconductive structures 306 a, 306 b includes a respective Cu pillar 330a, 330 b on an upper surface of substrate 304, and a respective upperaluminum contact structure 316 a, 316 b on an upper surface of Cupillars 330 a, 330 b. Upper aluminum contact structures 316 a, 316 b maybe electroplated or sputtered onto the respective upper surfaces of Cupillars 330 a, 330 b. As shown, semiconductor element 308 has been moveddownward through the motion of bonding tool 324 (as shown by the arrowsin FIG. 3) so that FIG. 3 illustrates contact between conductivestructures 306 a, 322 a and 306 b, 322 b. Ultrasonic energy (withoptional heat and/or bond force) is applied to upper semiconductorelement 308 (e.g., through bonding tool 324) using an ultrasonictransducer to form ultrasonic bonds between aluminum conductivestructures 322 a, 322 b and respective aluminum contact structures 316a, 316 b.

FIG. 4A illustrates portions of ultrasonic bonding machine 400,including bonding tool 424 and support structure 450. Uppersemiconductor element 408 is retained (e.g., by vacuum) by holdingportion 410 of bonding tool 424, and includes upper conductivestructures 412 a, 412 b (i.e., e.g., sputtered aluminum bumps, aluminumstud bumps, etc.) on a lower surface thereof. Lower semiconductorelement 460 includes semiconductor die 402 bonded to (or otherwisesupported by) support structure 404 (e.g., an FR4 support structure).Lower conductive structures 406 a, 406 b (i.e., e.g., sputtered aluminumbumps, aluminum stud bumps, etc.) are provided on an upper surface oflower semiconductor die 402. Substrate 404 in turn is supported bysupport structure 450. In the configuration shown in FIG. 4A, each ofupper conductive structures 412 a, 412 b are generally aligned with (andconfigured to be ultrasonically bonded to) opposing respective lowerconductive structures 406 a, 406 b. A detail of structures 412 a, 406 a(before ultrasonic bonding) is shown in FIG. 4B. Referring again to FIG.4A, semiconductor element 408 has been moved downward through the motionof bonding tool 424 (as shown by the arrows in FIG. 4A) so that contactis shown between conductive structures 406 a, 412 a and 406 b, 412 b.Ultrasonic energy 414 (with optional heat and/or bond force) is appliedto upper semiconductor element 408 (e.g., through bonding tool 424)using an ultrasonic transducer to form ultrasonic bonds 428 a, 428 bbetween deformed upper aluminum conductive structures and respectivedeformed lower aluminum contact structures (see, e.g., completedultrasonic bond 428 a′ formed between deformed structure 412 a′ anddeformed structure 406 a′ as illustrated in FIG. 4C).

FIG. 5A illustrates portions of ultrasonic bonding machine 500,including bonding tool 524 and support structure 550. Uppersemiconductor element 508 retained (e.g., by vacuum) by holding portion510 of bonding tool 524, and includes upper conductive structures 522 a,522 b (i.e, conductive aluminum pads 522 a, 522 b). Lower semiconductorelement 560 includes semiconductor die 502 bonded to (or otherwisesupported by) substrate 504 (e.g., an FR4 support structure). Lowerconductive structures 506 a, 506 b (i.e., e.g., sputtered aluminumbumps, aluminum stud bumps, etc.) are provided on an upper surface oflower semiconductor die 502. Substrate 504 in turn is supported bysupport structure 550. In the configuration shown in FIG. 5A, each ofupper conductive structures 522 a, 522 b are generally aligned with (andconfigured to be ultrasonically bonded to) opposing respective lowerconductive structures 506 a, 506 b. A detail of structures 522 a, 506 a(before ultrasonic bonding) is shown in FIG. 5B. As shown, semiconductorelement 508 has been moved downward through the motion of bonding tool524 (as shown by the arrows in FIG. 5A) so that FIG. 5A illustratescontact between conductive structures 506 a, 522 a. Ultrasonic energy(with optional heat and/or bond force) is applied to upper semiconductorelement 508 (e.g., through bonding tool 424) using an ultrasonictransducer to form ultrasonic bonds 528 a, 528 b between deformed upperaluminum conductive structures and respective deformed lower aluminumcontact structures (see, e.g., completed ultrasonic bond 528 a′ formedbetween deformed structure 522 a′ and deformed structure 506 a′ asillustrated in FIG. 5C).

FIG. 6A illustrates the ultrasonic bonding machine 600, includingbonding tool 624 and support structure 650. In FIG. 6, a plurality ofsemiconductor elements have been bonded together in a stackedconfiguration, in accordance with the teachings of the presentinvention. Specifically, semiconductor element 660 a includessemiconductor die 602 a bonded to (or otherwise supported by) substrate604 a, where conductive structures 606 a, 606 b (i.e., e.g., sputteredaluminum bumps, aluminum stud bumps, etc.) are provided on an uppersurface of semiconductor die 602 a. Semiconductor element 660 a issupported by support structure 650.

Another semiconductor element 660 b (including a correspondingsemiconductor die 602 b bonded to, or otherwise supported by, substrate604 b—and including conductive structures 612 a, 612 b on substrate 604b) has been previously been bonded to semiconductor element 660 a. Morespecifically, bonding tool 624 previously bonded (e.g., ultrasonicallybonded) element 660 b to element 660 a such that ultrasonic bonds 628 a,628 b were formed between respective pairs of aluminum conductivestructures 612 a, 606 a and 612 b, 606 b. Element 660 b also includesconductive structures 606 a′, 606 b′ which have been bonded toconductive structures of element 660 c in a step described below. FIG.6B illustrates a detailed view of ultrasonic bond 628 a includingdeformed conductive structures 612 a, 606 a.

Likewise, another semiconductor element 660 c (including a correspondingsemiconductor die 602 c bonded to, or otherwise supported by, substrate604 c—and including conductive structures 612 a′, 612 b′ on substrate604 c) has been previously been bonded to semiconductor element 660 b.More specifically, bonding tool 624 previously bonded (e.g.,ultrasonically bonded) element 660 c to element 660 b such thatultrasonic bonds 628 a′, 628 b′ were formed between respective pairs ofaluminum conductive structures 612 a′, 606 a′ and 612 b′, 606 b′.Element 660 c also includes conductive structures 606 a″, 606 b″ whichwill be bonded to conductive structures of element 660 d in a stepdescribed below.

As shown in FIG. 6A, upper semiconductor element 660 d is retained(e.g., by vacuum) by holding portion 610 of bonding tool 624, andincludes semiconductor die 602 d bonded to (or otherwise supported by)substrate 604 d. Conductive structures 612 a″, 612 b″ (i.e., e.g.,sputtered aluminum bumps, aluminum stud bumps, etc.) are provided on alower surface of substrate 604 d. Conductive structures 612 a″, 612 b″are generally aligned with (and configured to be ultrasonically bondedto) opposing respective conductive structures 606 a″, 606 b″.Semiconductor element 660 d is moved downward through the motion ofbonding tool 624 (as shown by the arrows in FIG. 6A). Following thisdownward motion, contact will occur between respective pairs ofconductive structures 612 a″, 606 a″ and 612 b″, 606 b″ (see, e.g., theFIG. 6C detailed view of contact between structures 612 a″, 606 a″ priorto deformation through ultrasonic bonding). Ultrasonic energy is appliedto upper semiconductor element 604 d through bonding tool 624 using anultrasonic transducer (not shown) to form the ultrasonic bonds betweenrespective pairs of conductive structures 612 a″, 606 a″ and 612 b″, 606b″.

While specific exemplary upper and lower aluminum conductive structureshave been illustrated, one skilled in the art would understand that avariety of shapes and designs of upper and lower aluminum conductivestructures are permissible within the teachings of the presentinvention.

FIG. 7 is a flow diagram illustrating a method of bonding semiconductorelements together in accordance with an exemplary embodiment of thepresent invention. As is understood by those skilled in the art, certainsteps included in the flow diagram may be omitted; certain additionalsteps may be added; and the order of the steps may be altered from theorder illustrated. At Step 700, a first semiconductor element (e.g.,including a semiconductor die on a substrate) is supported on a supportstructure of a bonding machine. The first semiconductor element (e.g.,an upper surface of the semiconductor structure) includes a plurality offirst conductive structures that are at least partially comprised ofaluminum (see, e.g., structures 106 a, 106 b of element 160 in FIG. 1A;structures 206 a, 206 b of element 260 in FIG. 2A; structures 306 a, 306b of element 360 in FIG. 3A; structures 406 a, 406 b of element 460 inFIG. 4A; structures 506 a, 506 b of element 560 in FIG. 5A; andstructures 606 a″, 606 b″ of element 660 c in FIG. 6A). At Step 702, asecond semiconductor element is retained by a holding portion of abonding tool of the bonding machine (see, e.g., elements 108, 208, 308,408, 508, and 660 d in the corresponding figures). The secondsemiconductor element includes a plurality of second conductivestructures (e.g., on a lower surface of the second semiconductorelement) that are at least partially comprised of aluminum. At Step 704,the first conductive structures and the second conductive structures arealigned with one another (see, e.g., FIGS. 1A and 6A) and are thenbrought into contact with one another. At optional Step 706, theplurality of aligned first conductive structures and second conductivestructure are pressed together with a predetermined amount of bondforce. The predetermined amount of bond force may be a single bond forcevalue, or may be a bond force profile where the actual bond force isvaried during the bonding operation. At optional Step 708, heat isapplied to the plurality of aligned first conductive structures and/orsecond conductive structures. For example, heat may be applied to thefirst conductive structures using the support structure that supportsthe first semiconductor element. Likewise, heat may be applied to thesecond conductive structures using the bonding tool that retains thesecond semiconductor element At Step 710, the plurality of firstconductive structures and second conductive structures areultrasonically bonded together to form ultrasonic bonds therebetween.

As will be appreciated by those skilled in the art, the presentinvention has particular benefits when an ambient/lower temperaturebonding operation is desired as the present invention bonds aluminummaterials to aluminum materials which may be readily accomplished withultrasonic energy and/or bond force, often without the need for heat.

Although the present invention has been illustrated and describedprimarily with respect to two pairs of conductive structuresultrasonically bonded together, it is of course not limited thereto. Inpractice, semiconductor packages (e.g., advanced packages) assembled inaccordance with the present invention may have any number of conductivestructures, and may have hundreds of pairs (or even thousands) ofconductive structures ultrasonically bonded together. Further, theconductive structures need not be bonded in pairs. For example, onestructure may be bonded to two or more opposing structures. Thus, anynumber of conductive structures from one semiconductor element may beultrasonically bonded to any number of conductive structures of anothersemiconductor element.

Although the present invention primarily describes (and illustrates) theapplication of ultrasonic energy through a bonding tool (e.g., where thebonding tool is engaged with an ultrasonic transducer), it is notlimited thereto. Rather, the ultrasonic energy may be transmittedthrough any desired structure, such as for example the supportstructure.

As will be appreciated by those skilled in the art, the details of theultrasonic bonding may vary widely depending on the specificapplication. Nonetheless, some non-limiting exemplary details are nowdescribed. For example, the frequency of the ultrasonic transducer maybe designed in connection with the design of the conductive structures(e.g., pillar structures, etc.), such that a transducer resonantfrequency substantially coincides with a resonant frequency of the givensemiconductor element—in this regard, the conductive structures may actdynamically as a cantilever beam. In another exemplary alternative, thetransducer may be operated at an off-resonant condition relative to thesemiconductor element in a simple “driven” type fashion.

Exemplary ranges for the energy applied to the ultrasonic transducer(e.g., applied to piezoelectric crystals/ceramics in the transducerdriver) may be in the range of 0.1 kHz-160 kHz, 10 kHz-120 kHz, 20kHz-60 kHz, etc. A single frequency may be applied, or a plurality offrequencies may be applied during bonding (e.g., sequentially,simultaneously, or both). The scrub of the semiconductor element (i.e.,vibrational energy applied to the semiconductor element held by thebonding tool) may be applied in any of a number of desired directions,and may be applied: through a bonding tool holding a semiconductorelement (as illustrated herein); through a support structure supportinga semiconductor element; amongst other configurations. Referringspecifically to the embodiments illustrated herein (where the ultrasonicenergy is applied through a bonding tool holding a semiconductorelement), the scrub may be applied in a direction substantially parallelto, or substantially perpendicular to, a longitudinal axis of the bondtool (or in other directions).

The vibrational energy applied by the ultrasonic transducer may beapplied, for example, in the peak-to-peak amplitude range of 0.1 um to10 um (e.g., with feedback control of constant voltage, constantcurrent, or alternate control schemes including but not limited toramped current, ramped voltage, or proportional feedback control basedon one or more inputs).

As described herein, bond force may also be applied during at least aportion of the ultrasonic bonding cycle. An exemplary range for the bondforce is 0.1 kg to 100 kg. The bond force may be applied as a constantvalue, or may be a bond force profile that changes during the bondingcycle. In a controlled bond force implementation, the feedback controlof the bond force may be constant, ramped or proportional based on oneor more inputs (e.g., ultrasonic amplitude, time, velocity, deformation,temperature, etc).

As described herein, one or more of the semiconductor elements may beheated prior to and/or during the bond cycle. An exemplary range of thetemperature of a semiconductor element is between 20° C.-250° C. Theheat (e.g., applied through one or both of the bond tool and the supportstructure, or other elements) may be applied as a constant value, or maybe a temperature profile that changes during the bonding cycle—and maybe controlled using feedback control.

Although the present invention has been illustrated and describedprimarily with respect to forming ultrasonic bonds between aluminumconductive structures on respective semiconductor elements, it is ofcourse not limited thereto. That is, the teachings of the presentinvention may have applicability in forming ultrasonic bonds betweenconductive structures having varying compositions. An exemplary list ofmaterials for the conductive structures being joined includes: aluminumto copper (i.e., forming ultrasonic bonds between aluminum conductivestructures on one semiconductor element to copper conductive structureson another semiconductor element); lead free solder (e.g., primarilycomposed of tin) to copper; lead free solder to aluminum; copper tocopper; aluminum to silver; copper to silver; aluminum to gold; andcopper to gold. Of course, other combinations of conductive structurecompositions (e.g., indium) are contemplated.

Although the invention is illustrated and described herein withreference to specific embodiments, the invention is not intended to belimited to the details shown. Rather, various modifications may be madein the details within the scope and range of equivalents of the claimsand without departing from the invention.

What is claimed:
 1. A method of ultrasonically bonding semiconductorelements, the method comprising the steps of: (a) aligning surfaces of aplurality of first conductive structures of a first semiconductorelement to respective surfaces of a plurality of second conductivestructures of a second semiconductor element, wherein the surfaces ofeach of the plurality of first conductive structures and the pluralityof second conductive structures is formed of copper; and (b)ultrasonically bonding ones of the first conductive structures torespective ones of the second conductive structures.
 2. The method ofclaim 1 wherein the first semiconductor element is a semiconductor die.3. The method of claim 1 wherein each of the first semiconductor elementand the second semiconductor element is a respective semiconductor die.4. The method of claim 1 wherein the first semiconductor elementincludes a semiconductor die.
 5. The method of claim 1 wherein each ofthe first semiconductor element and the second semiconductor elementincludes a respective semiconductor die.
 6. The method of claim 1further comprising the step of moving the first semiconductor elementtowards the second semiconductor element such that lower surfaces of thefirst conductive structures contact upper surfaces of the respectivesecond conductive structures.
 7. The method of claim 1 furthercomprising the step of applying pressure between the first semiconductorelement and the second semiconductor element during at least a portionof step (b).
 8. The method of claim 1 further comprising the step ofdeforming ones of the first conductive structures during step (b). 9.The method of claim 1 wherein step (b) is conducted at ambienttemperature.
 10. The method of claim 1 further comprising the step ofheating at least one of the first semiconductor element and the secondsemiconductor element during at least a portion of step (b).
 11. Themethod of claim 1 further comprising the step of heating the firstsemiconductor element, during at least a portion of step (b), using abonding tool that retains the first semiconductor element.
 12. Themethod of claim 1 further comprising the step of heating the secondsemiconductor element, during at least a portion of step (b), using asupport structure that supports the second semiconductor element duringstep (b).
 13. The method of claim 1 wherein at least one of theplurality of first conductive structures and the plurality of secondconductive structures includes a plurality of copper pillar structures.14. The method of claim 1 wherein each of the plurality of firstconductive structures and the plurality of second conductive structuresincludes a plurality of copper pillar structures.
 15. The method ofclaim 1 wherein step (b) includes ultrasonically bonding the ones of thefirst conductive structures to the respective ones of the secondconductive structures using a bonding tool that retains the firstsemiconductor element during step (b).
 16. The method of claim 15wherein the bonding tool is engaged with an ultrasonic transducer forproviding ultrasonic energy during step (b).
 17. The method of claim 15wherein the bonding tool retains the first semiconductor element duringstep (b) using vacuum.
 18. A semiconductor device comprising: (a) afirst semiconductor element including a plurality of first conductivestructures, the plurality of first conductive structures being formed ofcopper; and (b) a second semiconductor element including a plurality ofsecond conductive structures, the plurality of second conductivestructures being formed of copper, wherein the contact portions of onesof the plurality of first conductive structures are in contact with, andare ultrasonically bonded to, respective ones of the contact portions ofthe plurality of second conductive structures, wherein each of the firstsemiconductor element and the second semiconductor element includes arespective semiconductor die.
 19. The semiconductor device of claim 18wherein the first semiconductor element is a semiconductor die.
 20. Thesemiconductor device of claim 18 wherein each of the first semiconductorelement and the second semiconductor element is a respectivesemiconductor die.
 21. The semiconductor device of claim 18 wherein thefirst semiconductor element includes a semiconductor die.
 22. Thesemiconductor device of claim 18 wherein at least one of the pluralityof first conductive structures and the plurality of second conductivestructures are copper pillar structures.
 23. The semiconductor device ofclaim 18 wherein each of the plurality of first conductive structuresand the plurality of second conductive structures are copper pillarstructures.